A source close to the Huntsman campaign said the former ambassador to China and Utah Governor was “proud of the race that he ran” but “did not want to stand in the way” of rival Mitt Romney, the current front-runner for the Republican nomination.

After a disappointing third place finish in New Hampshire – a contest on which he had staked his candidacy – Huntsman vowed to fight on. In his concession speech in New Hampshire, he told his supporters: “I say third place is a ticket to ride, ladies and gentleman! Hello, South Carolina!”

But just six days from the South Carolina primary, Huntsman has said goodbye to the Palmetto state after all.

A Huntsman aide tells ABC News that the decision came in the wake of the results in the New Hampshire primary.

“He has been discussing with his family after they woke up after a successful evening in New Hampshire. They felt good about their performance in New Hampshire, but he and his family had a discussion and this is the decision came to,” the aide said. “At the end of the day he decided he did not want to hurt the best chance of beating Barack Obama and that’s Mitt Romney. By continuing into South Carolina and Florida, that’s what he would have been doing.”

While Huntsman will be throwing his support to Romney on Monday, it was only a week ago that he told ABC’s John Berman just the opposite.

Earlier this month, he told another ABC reporter that Romney is “completely out of touch.”

And as recently as Saturday, Huntsman was questioning Romney’s electability.

Reporters asked Huntsman if any of the Republican establishment had reached out to him and asked him to tone down his criticism of Romney and his work with Bain Capital. Huntsman explained: “Nope. And listen. I have said what I have said. My problem is really a political issue. And that is, when you have a candidate that talks about enjoyment in firing people, talks about pink-slips, who makes comment that seem to be so detached from the problems that Americans are facing today. that makes you pretty much unelectable. And I say, we want a nominee who can actually go on to win. That’s the issue…. the bigger issue is one of electability.”

Huntsman is now the fourth Republican candidate to drop out of the campaign. Tim Pawlenty, the former governor Minnesota, dropped out last summer after a disappointing finish in the Iowa straw poll. Rep. Michele Bachmann of Minnesota dropped out just after the Iowa Caucus and businesman Herman Cain left the race in a storm of sexual harassment allegations. With Huntsman’s endorsement of Romney on Monday as well as Pawlenty’s endorsement of Romney last summer, two of the four have thrown their support behind the former Massachusetts governor. The other two – Cain and Bachmann – have yet to endorse.